Multi-wheel vehicle

ABSTRACT

A vehicle comprises a steering operation device, a pair of running-driving wheels, which differentially drive when the steering operation device is manipulated, a pair of steerable running wheels interlocking with the steering operation device, and a steering mechanism interposed between the steering operation device and the pair of running-driving wheels. The steering mechanism includes a pair of drive gears interlocking with the steering operation device and a pair of follower gears interlocking with the respective steerable running wheels. The drive gears mesh with the respective follower gears so as to control lateral turning of the respective steerable running wheels. A gear radius of the drive gear may be greater than that of the follower gear meshing with it. A gear ratio between the mutually meshing drive and follower gears may be variable. The lateral turning centers of both the steerable running wheels may coincide with each other, and further coincide with a lateral turning center of the vehicle body caused by differential rotation of the running-driving wheels.

REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. application Ser. No.11/209,764, filed Aug. 24, 2005, which is a Continuation of U.S.application Ser. No. 10/252,837, filed Sep. 24, 2002, now U.S. Pat. No.6,951,259, which is a Continuation-in-Part of application Ser. No.09/820,673, filed Mar. 30, 2001, now U.S. Pat. No. 6,554,085, which is aContinuation-in-Part of application Ser. No. 09/372,747, filed Aug. 11,1999, now U.S. Pat. No. 6,336,513, the disclosures of which are allincorporated herein in their entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vehicle comprising a steeringoperation means, a pair of running-driving wheels which aredifferentially driven when the steering operation means is operated forcornering, and a pair of steerable running wheels interlocking with thesteering operation means.

2. Background Art

Conventionally, technology where a pair of hydrostatic transmissions(HSTs) are laterally connected, driving axles project laterally fromrespective HSTs, running-driving wheels are fixed to the outer ends ofboth axles, wherein movable swash plates as capacity adjusting membersfor the hydraulic pumps of the HSTs are individually changed in anglethereby driving the left and right running wheels individually, iswell-known, as disclosed in, for example, the U.S. Pat. No. 4,782,650.

In such construction, running speeds of the left and right HSTs, whenthe vehicle is driven straight forward, are equalized, and, when turned,are different.

The above-said vehicle, however, could not travel straight-forwardunless the output rotations of left and right HSTs completely coincidedwith each other, adjustments in shipment took much time, and parts andassembly errors had to be diminished so as to improve accuracy. Also,when there was a difference between the capacities of hydraulic pumpsand motors, left or right turning feeling of the vehicle was different,resulting in that the vehicle was very hard to steer.

Thus, for overcoming the above problems, a vehicle including a steeringoperation means; a pair of running-driving axles; a pair of runningwheels drivingly connected with the pair of running-driving axles; afirst differential unit interposed between the pair of running-drivingaxles; a first hydrostatic transmission for transmitting a driving forceto the first differential unit; a pair of steering output shafts; asecond differential unit interposed between the pair of steering outputshafts; a second hydrostatic transmission for transmitting a drivingforce to the second differential unit; a first drive train interposedbetween one of the steering output shafts and one of the running-drivingaxles, and a second drive train interposed between the other steeringoutput shaft and the other running-driving axle for transmitting therotating effort to the other running-driving axle in the oppositedirection to the first drive train, wherein the second hydrostatictransmission operationally interlocks with the steering operation meansso that the output speed and direction of the second hydraulictransmission is changed by manipulation of the steering operation means,has come to be invented. The vehicle does not require such labor asabove mentioned for precise coincidence between the capacities of thefirst and second hydrostatic pumps and motors. Also, when both thehydrostatic pumps and motors are arranged in a longitudinal line, thevehicle becomes laterally compact.

It is still desirable to improve the running efficiency of such avehicle when it drives and turns on a rough road or a soft ground. Ifthe vehicle is provided with a caster in addition to the pair of runningwheels, it can turn in a small circle, however, cornering on a roughroad or a slope becomes unstable. It is good for steady cornering thatthe vehicle has steerable running wheels which can be turned laterallyby operating the steering operation means. However, the steerablerunning wheels restrict the reduction of cornering circle. It isimpossible for the steerable running wheels to have such a smallcornering circle that can be ensured by casters. Especially, it isfurther hard for the vehicle to turn on a determined radius circlesteadily when the vehicle has a plurality of running wheels arranged ina longitudinal direction so as to be made larger in whole length.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a vehicle having a pairof running-driving wheels controlled by manipulation of a steeringoperation device such as a steering wheel so as to rotate differentiallyfor turning the vehicle right or left, and having a pair of steerablerunning wheels which are laterally turned by manipulation of thesteering operation device, wherein the lateral turning angles of thesteerable running wheels are amplified so as not to hinder the turningof the vehicle caused by the differential rotation of therunning-driving wheels.

To achieve the object, a steering mechanism interposed between the pairof steerable running wheels and the steering operation device turns thepair of steerable running wheels laterally according to increase of themanipulated degree of the steering operation device from its positionfor setting the vehicle into straight traveling so as to increase anincreasing rate of turning angle of one of the steerable running wheelsserving as an inside wheel disposed at inside of the turning vehicle inrelation to a unit of the manipulated degree of the steering operationdevice.

The steering mechanism turns the pair of steerable running wheelslaterally according to manipulation of the steering operation device forturning the vehicle right or left so as to make the turning angle of thesteerable running wheel serving as the inside wheel greater than theturning angle of the other steerable running wheel serving as an outsidewheel disposed at outside of the turning vehicle. Furthermore, thesteering mechanism may turn the pair of steerable running wheelslaterally according to increase of the manipulated degree of thesteering operation device so as to reduce an increasing rate of turningangle of the steerable running wheels serving as the outside wheel inrelation to a unit of the manipulated degree of the steering operationdevice.

The steering mechanism turns the pair of steerable running wheelslaterally according to manipulation of the steering operation device sothat lateral turning centers of the respective steerable running wheelscoincide with each other at a point on a line along which therunning-driving wheels are disposed coaxially. The common turning centerof both the steerable running wheels moves on the line toward the middleposition between the right and left running-driving wheels according toincrease of the manipulated degree of the steering operation device.Furthermore, the common lateral turning center of both the steerablerunning wheels moves so as to coincide with a turning center of thevehicle caused by differential rotation of the running-driving wheelsmoving on the line.

The steering mechanism includes a pair of drive gears interlocking withthe steering operation device so as to be rotated by manipulation of thesteering operation device, and a pair of follower gears interlockingwith the respective steerable running wheels so as to be rotatedtogether with the respective steerable running wheels. The followergears mesh with the respective drive gears so as to make two couples ofmutually meshing drive and follower gears. Gear ratios of the respectivecouples of mutually meshing drive and follower gears vary according tomanipulation of the steering operation device.

The gear ratio is a radius ratio of the drive gear to the follower gear.The gear ratio of the mutually meshing drive and follower gearsinterlocking with one of the steerable running wheels serving as theinside wheel is increased according to increase of the manipulateddegree of the steering operation device. The gear ratio of the mutuallymeshing drive and follower gears interlocking with the other of thesteerable running wheels serving as the outside wheel is reducedaccording to increase of the manipulated degree of the steeringoperation device.

The drive gears and the follower gears may be spur gears. Alternatively,the drive gears and the follower gears may be bevel gears.

A gear radius of the drive gear is greater than that of the followergear meshing with the drive gear.

The pair of running-driving wheels are disposed coaxially to each otheralong a line. The couples of mutually meshing drive and follower gearsare so arranged as to make the lateral turning centers of the respectivesteerable running wheels coincide with each other at a point on theline. The common turning center of both the steerable running wheelsmoves on the line toward the middle position between the right and leftrunning-driving wheels according to increase of the manipulated degreeof the steering operation device. The common lateral turning center ofboth the steerable running wheels moves so as to coincide with a turningcenter of the vehicle caused by differential rotation of therunning-driving wheels moving on the line.

The steering mechanism may include a hydraulic power steering device.The hydraulic power steering device may rotate the drive gears.

These and other objects of the invention will become more apparent inthe detailed description and examples which follow.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an axle driving/steering unit 10 forthe present invention.

FIG. 2 is a schematic diagram showing a modified embodiment of axledriving/steering unit 10 of FIG. 1.

FIG. 3 is a schematic view of a six-wheel vehicle having first wheels 43driven by axle driving/steering unit 10, castors 16 and third wheels 45as a multi-axle vehicle according to the present invention.

FIG. 4 is a schematic view of the six-wheel vehicle of FIG. 3, whereincastors 16 and third wheels 45 are exchanged with each other.

FIG. 5 is a schematic view of the six-wheel vehicle of FIG. 3, whereinsteerable running wheel structure 17 replaces castors 16.

FIG. 6 is a schematic view of a six-wheel vehicle having first wheels 43and two pair of steerable running wheels 18 and 19.

FIG. 7 is a schematic view of a four-wheel vehicle as a preferredembodiment of a multi-axle vehicle having first drive wheels 43 andsecond drive wheels 46 drivingly connected with each other.

FIG. 8 is a schematic view of a six-wheel vehicle as the vehicle of FIG.7 further provided with castors 16.

FIG. 9 is a schematic view of the six-wheel vehicle of FIG. 7, whereincastors 16 and third wheels 45 are exchanged with each other.

FIG. 10 is a schematic view of the six-wheel vehicle of FIG. 7, whereinsteerable running wheels 18 replace castors 16.

FIG. 11 is a schematic view of a four-wheel vehicle having steerabledrive wheels 47 driven by axle driving/steering unit 10 and turned bymanipulation of a steering wheel 14, wherein castors 16 are provided.

FIG. 12 is a schematic view of a four-wheel vehicle having steerabledrive wheels 47, wherein second drive wheels 46 drivingly connected withsteerable drive wheels 47 are provided.

FIG. 13 is a schematic view of a six-wheel vehicle having steerabledrive wheels 47 as the vehicle of FIG. 12 further provided with castors16.

FIG. 14 is a schematic view of a four-wheel vehicle having steerabledrive wheels 47, wherein steerable running wheels 18 are provided.

FIG. 15 is a schematic view of a four-wheel vehicle similar with that ofFIG. 14, wherein the lateral turning direction of steerable drive wheels47 in accordance with the manipulation of steering wheel 14 can beswitched.

FIG. 16 is a schematic view of a four-wheel vehicle having steerabledrive wheels 47, wherein steerable running wheels 19 also serving assecond drive wheels 46 are provided.

FIG. 17 is a schematic view of a six-wheel vehicle having steerabledrive wheels 47, steerable running wheels 18 and second drive wheels 46.

FIG. 18 is a schematic view of a six-wheel vehicle having steerabledrive wheels 47, castors 16, and steerable running wheels 19 alsoserving as second drive wheels 46.

FIG. 19 is a schematic view of the six-wheel vehicle of FIG. 18, whereinsteerable running wheels 18 replace castors 16.

FIG. 20 is a schematic view of a four-wheel vehicle having steerabledrive wheels 47 and second drive wheels 46, wherein second drive wheels46 are drivingly connected with steerable drive wheels 47 throughanother transmitting structure.

FIG. 21 is a diagrammatic plan view of a four-wheel running vehicleprovided with a steering linkage 100 which turns left and rightsteerable running wheels 41L and 41R while amplifying the lateralturning angle of wheels 41L and 41R in connection with operation of axledriving/steering apparatus 10.

FIG. 22 is a diagrammatic plan view of a four-wheel running vehicleprovided with steering linkage 100 including a hydraulic power steeringcylinder 113.

FIG. 23 is a diagrammatic plan view of a six-wheel running vehicleprovided with steering linkage 100 which turns left and right steerablerunning wheels 41L and 41R while amplifying the lateral turning angle ofwheels 41L and 41R in connection with operation of axle driving/steeringapparatus 10.

FIG. 24 is a rear view of right and left steering gear units 101R and101L constituted by spur gears 38 and 39, interlocking with right andleft steerable running wheels 41R and 41L, respectively.

FIG. 25 is a plan view of steering gear unit 101 shown in FIG. 23.

FIG. 26 is the same view with FIG. 24, wherein cranked kingpins 116support respective steerable running wheels 41R and 41L.

FIG. 27 is a rear view of right and left steering gear units 101R and101L constituted by bevel gears 82 and 83, interlocking with right andleft steerable running wheels 41R and 41L, respectively.

FIG. 28 is a side view of steering gear unit 101 shown in FIG. 27.

FIG. 29 is a plan view of steering gear unit 101 shown in FIG. 27.

FIG. 30 is a rear view of modified right and left steering gear units101R and 101L constituted by bevel gears 82 and 83, interlocking withright and left steerable running wheels 41R and 41L, respectively.

FIG. 31 is a rear view of further modified right and left steering gearunits 101R and 101L constituted by bevel gears 82 and 83, interlockingwith right and left steerable running wheels 41R and 41L, respectively,wherein the rotational force of a steering wheel 14 is shared betweensteering gear units 101R and 101L through a differential mechanism 130.

FIG. 32(a) is a plan view of differential mechanism 130 shown in FIG. 31in connection with steering wheel 14 through a linkage.

FIG. 32(b) is a plan view of modification of differential mechanism 130shown in FIGS. 31 and 32(a).

FIG. 33 is a plan view of spur gears 104 and 114 having fixed radiiserving as spur gears 38 and 39 of steering gear unit 101.

FIG. 34 is a side view of bevel gears 84 and 85 having fixed radiiserving as bevel gears 82 and 83 of steering gear unit 101.

FIG. 35 is a front (rear) view of the same.

FIG. 36 is a plan view of spur gears 58 and 59 having variable radiiserving as spur gears 38 and 39 of steering gear unit 101.

FIG. 37 is a side view of bevel gears 175 and 176 having variable radiiserving as bevel gears 82 and 83 of steering gear unit 101.

FIG. 38 is a plan view of the same.

FIG. 39 is a front (rear) view of the same.

FIG. 40 illustrates graphs expressing variation of lateral turningangles of right and left steerable wheels 41 serving as an inside wheeland an outside wheel of a turning vehicle in relation to rotationalangle of steering wheel 14.

FIG. 41 is a diagrammatic plan view of a four-wheel running vehicleemploying variable gears 58 ad 59 serving as steering gear units 101Rand 101L, wherein the vehicle travels straight forward.

FIG. 42 is a diagrammatic plan view of the same, wherein steering wheel14 is rotated leftward a little so that left running-driving wheel 43Lrotates forward at a reduced speed.

FIG. 43 is a diagrammatic plan view of the same, wherein steering wheel14 is rotated leftward so greatly as to eliminate the rotary speed ofleft running-driving wheel 43L.

FIG. 44 is a diagrammatic plan view of the same, wherein steering wheel14 is fully rotated leftward so that left running-driving wheel 43Lrotates backward.

FIG. 45 is a diagrammatic plan view of a six-wheel running vehicleemploying variable gears 58 ad 59 serving as steering gear units 101Rand 101L, wherein the vehicle travels straight forward.

FIG. 46 is a diagrammatic plan view of the same, wherein steering wheel14 is rotated leftward a little so that left running-driving and drivenwheels 43L and 43R rotate forward at a reduced speed.

FIG. 47 is a diagrammatic plan view of the same, wherein steering wheel14 is rotated leftward so greatly as to eliminate the rotary speed ofleft running-driving and driven wheels 43L and 46L.

FIG. 48 is a diagrammatic plan view of the same, wherein steering wheel14 is fully rotated leftward so that left running-driving and drivenwheels 43L and 46L rotate backward.

FIG. 49 is a plan view of a modification of variable spur gears 58 and59 modified so as to compensate for a difference between the lateralturning center of inside and outside steerable wheels 41 and the lateralturning center of the vehicle caused by differential drive of wheels 43,which occurs when the lateral turning center of the vehicle caused bydifferential drive of wheels 43 in relative to every rotational angle ofsteering wheel 14 cannot be conserved in correspondence to variation oftraveling speed of the vehicle.

FIG. 50 is a plan view of another modification of variable spur gears 58and 59 modified for the same purpose.

DETAILED DESCRIPTION OF THE INVENTION

An axle driving/steering unit 10 of the present invention can make itsleft and right running-driving wheels different in their rotary speedsthat a vehicle using it turns leftward and rightward. Driving/steeringunit 10 comprises a first running hydrostatic transmission (to be hereinafter called “a main driving HST”) 21 including a hydraulic pump andmotor fluidly connected with each other, a second steering hydrostatictransmission (to be herein after called “a steering HST”) 22 including ahydraulic pump and motor fluidly connected with each other, a steeringdifferential unit (a second differential unit) 23 for steering thevehicle, and a running differential unit (first differential unit) 24for running-driving the vehicle. Differential units 23 and 24 are eitherof a type as a combination of planetary gears and bevel gears or of atype as a combination of a pair of differential gears.

Referring to FIG. 1 showing axle driving/steering unit 10 usingplanetary gears and bevel gears, main driving HST 21 comprises avariable displacement hydraulic pump 52 and a fixed displacementhydraulic motor 53, as is well-known. An input shaft 26 as a pump shaftof hydraulic pump 52 projects from a housing 25 and a driving force istransmitted from an engine 11 through a belt 30 to an input pulley 27provided on input shaft 26 (refer to FIGS. 3-20 showing variousembodiments of a multi-axle vehicle having axle driving/steering unit10, except for some figures from which engine 11, belt 30 and the likeare omitted for convenience).

Hydraulic pump 52 and hydraulic motor 53 are fluidly connected with eachother by a closed circuit formed in a center section.

A movable swash plate 57, used as means for changing a discharge amountand a discharge direction of hydraulic oil from hydraulic pump 52, isconnected with a control shaft. The control shaft is connected through aconnecting means 28 like an arm or a link disposed outside housing 25with a speed change operation means like a lever or a pedal (in thisembodiment, a speed change pedal 15) provided on a vehicle. Speed changepedal 15 is pivotally supported at the center thereof onto the vehiclebody. When pedal 15 is trod at the front portion, the vehicle runsforwardly and is accelerated in proportion to its treading amount. Whenspeed change pedal 15 is trod at rear portion, the vehicle is drivenrearwardly.

Speed change pedal 15 is rotated to tilt movable swash plate 57 so as tochange the discharge direction and discharge amount of hydraulic oilfrom hydraulic pump 52, thereby changing the running speed.

Pressure oil from hydraulic pump 52 is sent to hydraulic motor 53through an oil passage in the center section so as to drive a motorshaft 54. A braking unit 66 is disposed on one side of motor shaft 54,which is an output shaft of hydraulic motor 53. Onto the other side ofmotor shaft 54 are fixed a running-driving gear 55 and a steering powertake-off gear 56. Running-driving gear 55 engages with a center gear 60fixed onto a shaft 44 disposed between driving axles 40L and 40R andcoaxially therewith. On both sides of shaft 44 are fixed sun gears 61Land 61R, which engage at the outer peripheries thereof with planetarygears 63 pivotally supported onto carriers 62 fixed to the inner ends ofrunning-driving axles 40L and 40R. Internal gears 64L and 64R engagewith planetary gears 63 around sun gears 61L and 61R. Large diametergears 65 integrally fixed with internal gears 64L and 64R are freelyfitted onto running-driving shafts 40L and 40R outside carriers 62.Thus, running differential unit 24 of a running-driving system isconstructed.

Steering power take-off gear 56 engages with an input gear 67 forsteering HST 22, input gear 67 being fixed on an input shaft 70 servingas a pump shaft for a hydraulic pump 71 of steering HST 22. Steering HST22 comprises a variable displacement hydraulic pump 71 and a fixeddisplacement hydraulic motor 72 and is mounted onto the center sectionfixed into housing 25. Both pump 71 and motor 72 are fluidly connectedwith each other through oil passages in the center section. A movableswash plate 76 of hydraulic pump 71 is interlockingly connected throughan arm 139 and a connection link 160 (refer to FIGS. 3-20) with asteering wheel 14 serving as a steering operation means provided on thevehicle, and tilts correspondingly to a rotation of steering wheel 14.Movable swash plate 76 tilts to change the discharge direction anddischarge amount of pressure oil from hydraulic pump 71 so as to enablemotor shaft 73 of hydraulic motor 72 to be changed in the direction andnumber of rotations thereof.

A bevel gear 74 is fixed at the upper end of motor shaft 73 of hydraulicmotor 72. A pair of side bevel gears 75L and 75R, disposed opposite toeach other, engage with bevel gear 74 so as to be rotated reversely toeach other. Small diameter gears 78 are fixed onto the outer ends of apair of steering output shafts 77 on which side bevel gears 75L and 75Rare fixedly supported, and engage with large diameter gears 86 a of twingears 86 free-fitted onto motor shaft 54. Small diameter gears 86 b oftwin gears 86 engage with large diameter gears 65, respectively, so asto transmit the driving force to steering differential unit 23.

In the above-mentioned construction, input shaft 26 is always driven inthe state that engine 11 is driven. When steering wheel 14 is put in thestraight forward running direction, steering HST 22 is in neutral andmotor shaft 73 of hydraulic motor 72 is not driven, so that speed changepedal 15 is trod at the front or the rear to turn movable swash plate 57for hydraulic pump 52 of main driving HST 21, thereby driving hydraulicmotor 53, whereby left and right running-driving axles 40L and 40R aredriven at equal rotational speed through motor shaft 54, running-drivinggear 55, center gear 60 and running differential unit 24, and thevehicle is straight forwardly or rearwardly driven. In the state offorwardly or rearwardly driving, hydraulic pump 71 of steering HST 22 isdriven from motor shaft 54 through gears 56 and 67 in proportion to therunning speed, thereby enabling the steering feeling correspondingthereto to be obtained by the operation as described later.

When steering wheel 14 is rotated in the straight forward running state,movable swash plate 76 of steering HST 22 is turned to drive hydraulicmotor 72.

For example, when steering wheel 14 is rightwardly turned, hydraulicpump 71 is actuated so as to drive hydraulic motor 72, so that thedriving force from motor shaft 73 is transmitted to left and right sidebevel gears 75L and 75R through bevel gear 74 in a manner that one ofside bevel gears 75L and 75R is normally rotated and the other isreversely rotated at equal rotational speed, and furthermore the drivingforce is transmitted to internal gears 64L and 64R through smalldiameter gears 78 and twin gears 86. The speed of normal rotation ofinternal gear 64L is added to that of normal revolution of planetarygears 63L normally rotating around sun gear 61L and the speed of reverserotation of internal gear 64R is deducted from that of normal revolutionof planetary gears 63R around sun gear 61R.

Thus, keeping the driving state of both running-driving axles 40L and40R, the rotational speed of driving axle 40L becomes larger than thatof driving axle 40R, thereby rightwardly turning the course of thevehicle.

A discharge amount of oil from hydraulic pump 71 increases accordinglyas the turning angle of steering wheel 14 becomes larger, andcorrespondingly, the rotary speed of hydraulic motor 72 increases in astepless manner, so that a difference of rotary speeds between left andright running-driving axles 40L and 40R gradually increases, therebyenabling the vehicle to be turned further in a smaller radius.

Conversely, when steering wheel 14 is leftwardly turned, movable swashplate 76 of steering HST 22 is tilted in the reverse direction to theabove-mentioned, whereby the output rotation direction of hydraulicmotor 72 becomes reversed so as to leftwardly turn the vehicle in thereverse direction to the above-mentioned case.

In a case when speed change pedal 15 is trod at the rear to rearwardlydrive the vehicle, speed change pedal 15 is rearwardly turned to turnmovable swash plate 57 reversely to the above-mentioned so as to rotatemotor shaft 54 reversely to its rotational direction for forwardmovement, thereby driving the vehicle rearwardly. In the case ofrearwardly running of the vehicle, when steering wheel 14 is rightwardlyrotated to tilt movable swash plate 76, hydraulic motor 72 and motorshaft 73 are rotated reversely to their rotational direction in the samecase when the vehicle runs forwardly because of the reverse rotation ofinput shaft 70 of steering hydraulic pump 71. Thus, left side bevel gear75L is rotated reversely so that its rotary speed is added to the speedof the reverse revolution of left planetary gears 63L, and right sidebevel gear 75R is rotated normally so that its rotary speed is deductedfrom the speed of reverse revolution of right planetary gears 63R,whereby the vehicle can rightwardly turn while rearwardly moving.Conversely, the vehicle, while rearwardly moving, can be turnedleftwardly by rotating steering wheel 14 leftwardly.

Accordingly, the vehicle, even when rearwardly driven, can turncorresponding to the rotating direction of steering wheel 14 so as to bedriven in the same feeling as an automobile. When speed change pedal 15is in a neutral position, i.e., when the vehicle stops, hydraulic motor53 is not driven, whereby steering hydraulic pump 71 is not driven, sothat, even when steering wheel 14 is rotated, hydraulic motor 72 is notdriven and the vehicle does not travel. Hence, even when the operatorwho gets in and out of a driver's seat in the vehicle touches steeringwheel 14, the vehicle remains stationary, thereby ensuring safety.

The steering differential unit and the running differential unit may, asshown in FIG. 2, both comprise differential gears. In this case, theinput shaft of steering HST 22 is directly connected onto motor shaft 54of main driving HST 21, and running-driving gear 55 fixed onto motorshaft 54 transmits the driving force to differential ring gear 92 ofrunning differential unit 24′ through gears 90 and 91. On motor shaft 73of steering HST 22 is fixed a spur gear 93, from which the driving forceis transmitted to differential ring gear 95 of a steering differentialunit 23′ through twin gears 94 fitted on right running-driving axle 40R.On the one hand, the driving force is transmitted through a reversinggear 98 from a left differential output gear 97L fixed onto leftsteering output shaft 96L of steering differential unit 23′ to a gear99L fixed onto left running-driving axle 40L, and on the other hand, thedriving force is transmitted from a right differential output gear 97Rfixed onto a right steering output shaft 96R of steering differentialunit 23′ to a gear 99R fixed onto right running-driving axle 40R.

Thus, as the same as above-mentioned, when steering wheel 14 isrightwardly turned, the normally rotational driving force is transmittedto left gear 99L, and when steering wheel 14 is leftwardly turned, thenormal rotational driving force is transmitted to right gear 99R.

However, it is possible to transmit the driving force by sprockets andchains instead of gears 97L, 97R and 99L, 99R. Also, it is possible thatmain driving HST 21 and running differential unit 24′ are housed in onehousing so as to be interlockingly connected, steering HST 22 andsteering differential unit 23′ are housed in another housing so as to beinterlockingly connected, and the output rotation from steeringdifferential unit 23′ is laterally and reversely transmitted to theoutput shafts (driving axles 40L and 40R) of running differential unit24′.

For application of axle driving/steering unit 10 to a vehicle, as shownin FIG. 3 and others, running-driving axles 40L and 40R are journalledby a vehicle chassis 12. Firstly, as shown in FIG. 1 and others, a pairof first running wheels 43 are fixed onto outer ends of respective axles40L and 40R. As shown in FIG. 3 and others, the steering operation means(steering wheel 14) is connected to an arm 139 for rotating movableswash plate 76 of steering HST 22 through gears in a steering gear box(not shown), a pitman arm 159 and a connection link 160. In the gear boxare housed reduction gears of conventional rack-and-pinion type or wormgear type, for converting the rotational motion of steering wheel 14into linear motion of pitman arm 159.

To further reduce the turning radius of a vehicle includingrunning-driving wheels which can be differentially driven by axledriving/steering system 10 interlocked with the steering operation tool(steering wheel 14), at least one castor, for example, may beadditionally provided on the vehicle before or behind first runningwheels 43 for serving as a second running wheel which is laterallyturned into the running direction of the vehicle. In each of FIGS. 3 and4, a pair of castors 16 are provided. In FIG. 3, castors 16 are disposedbefore first running wheels 43, and in FIG. 4, they are behind firstrunning wheels 43.

However, when the vehicle parks on a slope along the contour linethereof, the vehicle's weight acts to turn the castors in the tiltingdirection, whereby the vehicle body tilts down forwardly.

Therefore, in each of FIGS. 3 and 4, for increasing the gripping forceagainst the ground surface, in addition to castors 16, a pair of thirdrunning wheels 45 are fixed onto outer ends of respective second axles50L and 50R journalled by vehicle chassis 12 in parallel torunning-driving axles 43 and either before or behind first runningwheels 43. Incidentally, castors 16 are disposed oppositely to thirdrunning wheels 45 with respect to first running wheels 43. In FIG. 3,third running wheels 45 are behind first running wheels 43, and in FIG.4, they are in front of first running wheels 43.

Accordingly, the vehicle of each of FIGS. 3 and 4 is a six-wheelvehicle, wherein the pair of castors 16 are laterally turned into therunning direction of the vehicle in addition to the difference of rotaryspeed between left and right first running wheels 43 during the steeringof the vehicle so as to further reduce the turning radius of thevehicle, and on the other hand, the pair of third wheels 46 are providedso as to increase the traveling stability of the vehicle.

However, the castor is hard to be viewed by the operator because it isdisposed under a floor of the vehicle, and the castor is independent ofsteering wheel 14, whereby, in the state where the vehicle stops, it isdifficult to distinguish which direction the castors are in.

For example, in a case when the castor stops while leftwardly turning,then the vehicle starts while steering wheel 14 is rightwardly turned,the castors may instantaneously be turned from the left side to theright side, whereby the vehicle, for a moment, moves in the direction ofa letter S, resulting in the operator being misguided.

In order to solve the problem, steerable running wheels whose lateralturning depends upon the manipulation of steering wheel 14 may beprovided.

Referring to FIG. 5, instead of castors 16, a steerable running wheelstructure 17 is disposed in the lateral middle of the front portion ofthe vehicle of FIG. 3. The steerable running wheel structure 17comprises a pair of steerable running wheels 17 a and a lateral-rotationpivot 17 b arranged between the pair of steerable running wheels 17 a,similarly with the structure of a nose landing gear of a long-range jet.Lateral-rotation pivot 17 b is connected with steering wheel 14 througha linkage, an actuator and the like so as to be rotated by themanipulation of steering wheel 14, thereby laterally turning the pair ofsteerable running wheels 17 a. This structure is advantageous inreduction of the turning radius similarly with a single castor 16provided on the lateral middle portion of the vehicle. However, the pairof steerable running wheels 17 a have a greater gripping force than thesingle castor 16.

Furthermore, the direction of steerable running wheels 17 a can berecognized by viewing the position of steering wheel 14, thereby solvingthe above problem.

It is ordinary that a pair of steerable running wheels 18 which arelaterally turned by manipulation of steering wheel 14 are disposedbefore the pair of first running wheels 43. Referring to FIG. 6, a pairof steerable running wheels 19 are additionally arranged behind firstrunning wheels 43.

Front steerable running wheels 18 are supported to king pins 156 invehicle chassis 12 before axle driving/steering unit 10, knuckle arms156 are fixed to king pins 155, and left and right knuckle arms 156 arepivotally connected with each other through a tie rod 157. Tie rod 157is connected to one end of pitman arm 159, and the other end thereof isconnected in interlocking with a stem of steering wheel 14 through agear.

Rear steerable running wheels 19 are supported onto king pins 163rotatably supported onto vehicle chassis 12. Knuckle arms 164 are fixedto king pins 163 and pivotally connected with each other through a tierod 165. Tie rod 165 is connected to pitman arm 159 through a bell crankarm 167 and a connecting link 166.

Knuckle arms 156 and 164 and tie rods 157 and 165, when steering wheel14 is fully turned, tilt at about 80° in this embodiment.

Preferably, rear steerable running wheels 19 are laterally turned in thelateral opposite direction of the laterally turned front steerablerunning wheels 18.

Next, description will be given on various embodiments of a vehiclewherein the driving force of running-driving axles 40L and 40R istransmitted to other running wheels.

Referring to FIG. 7, a pair of left and right running-driven axles 150Land 150R as the second axles are rotatably supported by vehicle chassis12 in parallel to left and right running-driving axles 40L and 40R asaxles of first running wheels (first running-driving wheels) 43. A pairof second running-driving wheels 46 are fixed onto outer ends of axles150L and 150R.

Sprockets (or pulleys) 152 are fixed onto running-driving axles 40L and40R, and sprockets 153 are fixed onto running-driven axles 150L and150R, respectively, and a chain (or a belt) 154 is interposed betweeneach sprocket 152 and each sprocket 153 on the same side of the vehicle,so as to drive running-driven axles 150L and 150R in the same directionand at the same rotary speed with running-driving axles 40L and 40R.

In such the construction, a plurality of left and right running wheels(four wheels in the embodiment of FIG. 7) are simultaneously driven inthe same direction and in at equal rotational speed while the vehicle isrunning straight forward. When steering wheel 14 is rotated,running-driving wheels 43 and 46 on the turning side of steering wheel14 are accelerated, and opposite running-driving wheels 43 and 46 aredecelerated, whereby the vehicle turns left or right. Whether thevehicle runs straight or turns, all running wheels 43 and 46 are drivenso as to enable the vehicle to run effectively on rough or soft ground.Thus, the construction of this embodiment can be applied to, forexample, a skid steering loader, a carrier or an amphibious vehicle.Also, second running-driving wheels 46 are driven synchronously torespective first running-driving wheels 43 so as to prevent wheels 46from being dragged on the ground, thereby reducing the damage of theground.

Furthermore, each of FIGS. 8-10 shows a six-wheel vehicle additionallyprovided with a pair of running wheels which are laterally rotated intothe running direction of the vehicle during the steering of the vehicle.Referring to FIGS. 8 and 9, castors 16 are provided as such runningwheels. In FIGS. 8-10, of the six running wheels, first running-drivingwheels 43 are arranged at the longitudinal middle. Castors 16 serving assecond running wheels and second running-driving wheels 46 serving asthird running wheels are arranged in front of and behind firstrunning-driving wheels 43, respectively in FIG. 8, and behind and infront of wheels 43, respectively, in FIG. 9. Referring to FIG. 10,second running-driving wheels 46 are arranged behind firstrunning-driving wheels 43, and front steerable running wheels 18 turnedby steering wheel 14 are in front of first running-driving wheels 43similarly with FIG. 6.

In such constructions, when steering wheel 14 is rotated, the rotaryspeed of first and second running-driving wheels 43 and 46 on onelateral side becomes different from that of first and secondrunning-driving wheels 43 and 46 on the other lateral side.Simultaneously, castors 16 or steerable running wheels 18 are laterallyturned into the running direction of the vehicle oriented by steeringwheel 14. Accordingly, even when a whole length of vehicle body is madelarger, the vehicle can smoothly make a small turn. Also, the wheelsscarcely cause dragging while the vehicle is turning, thereby enablingthe vehicle to turn without roughening a field.

Referring to FIGS. 11-20, the first running wheels attached to outerends of respective running-driving axles 40L and 40R as output shafts ofaxle driving/steering unit 10 are steerable driving wheels 47 serving asrunning-driving wheels and also as steerable running wheels laterallyturned by steering wheel 14.

In this regard, steerable driving wheels 47 are supported onto king pins163 rotatably supported onto vehicle chassis 12. Knuckle arms 164 arefixed to king pins 163 and pivotally connected with each other through atie rod 165. Tie rod 165 is connected to pitman arm 159 through a bellcrank arm 167 and a connecting link 166. Pitman arm 159 is connected toarm 139 for rotating movable swash plate 76 of steering HST 22 throughconnection link 161 as mentioned above.

Due to such a construction, steering wheel 14 is manipulated (turnedleftward or rightward) so as to make the rotary speeds of left and rightsteerable driving wheels 47 driven by axle driving/steering unit 10different from each other, and simultaneously to make both steerabledriving wheels 47 turn laterally.

For an embodiment of a vehicle having such steerable driving wheels 47,firstly, FIG. 11 shows a vehicle having a pair of castors 16 in front ofleft and right steerable driving wheels 47 so as to be turnable on asmall circle.

The vehicle of FIG. 12 is a four-wheel vehicle having front steerabledriving wheels 47 as the first running-driving wheels, and rear secondrunning-driving wheels 46. The driving forces of left and rightrunning-driving axles 40L and 40R onto which steerable driving wheels 47are attached are transmitted through sprockets 152 and 153 and chains154 to respective left and right running-driven axles 150L and 150R ontowhich second running-driving wheels 46.

The vehicle of FIG. 13 serves as a combination of both embodiments ofFIGS. 11 and 12. In other words, this is a six-wheel vehicle providedwith a pair of second running-driving wheels 46, into which the drivingforces of steerable driving wheels 47 as the first running-drivingwheels, and a pair of castors 16.

FIG. 13 shows that castors 16, steerable driving wheels 47 and secondrunning-driving wheels 46 serve as front wheels, longitudinal middlewheels, and rear wheels, respectively. However, the positionalrelationship among wheels 16, 47 and 46 in the longitudinal direction ofthe vehicle is not limited to the embodiment shown.

The vehicle of each of FIGS. 14 and 15 is a four-wheel vehicle whereinthe pair of steerable driving wheels 47 are rear running wheels, and apair of left and right steerable running wheels 18 as shown in FIG. 6,which are turned laterally by manipulation of steering wheel 14, arefront running wheels.

Referring to FIG. 14, the lateral turning directions of steerabledriving wheels 47 and steerable running wheels 18 during the rotation ofsteering wheel 14 coincide with each other. In FIG. 15, they areopposite, that is, steerable running wheels 18 are turned laterally tothe side of rotated steering wheel 14 and steerable driving wheels 47are turned laterally oppositely to the side of rotated steering wheel14.

Referring to FIG. 15, a pivotal joint point between a T-like shaped bellcrank arm 167′ and connection link 166 can be positionally changed so asto change a lateral turning direction of rear steerable driving wheels47 with respect to the rotating direction of steering wheel 14,according to different running conditions. When the vehicle is to runfast or is to make a turn while keeping its posture in parallel,connection link 166 is disposed along a phantom line shown in FIG. 15 tobe connected to arm 167′, thereby constituting a linkage which issimilar with that consisting of connection link 166 and bell crank arm167 of the embodiment shown in FIG. 14, so that all front and rearrunning wheels 18 and 47 can be moved substantially in parallel, wherebythe road or field is prevented from being roughened, the turning radiuscan be diminished and side slip can be prevented. When the vehicle is tomake U-turn, for example, while farming on a narrow field, connectionlink 166 is disposed along a full line shown in FIG. 6 to be connectedto arm 167′, so that rear steerable driving wheels 47 are turnedlaterally opposite to the lateral turning direction of front steerablerunning wheels 18, whereby the vehicle can make a U-turn with a greatlyreduced radius without a large rotational degree of steering wheel 14.

It should be noted that, in both the embodiments shown in FIGS. 14 and15, the lateral turning angles of front and rear running wheels 18 and47 are determined in correspondence to the difference between the rotaryspeeds of left and right running-driving axles 40L and 40R driven byaxle driving/steering unit 10.

The vehicle of FIG. 16 is a four-wheel vehicle, wherein the pair ofsteerable driving wheels 47, which become different from each other intheir rotary speeds and are laterally turned during the manipulation ofsteering wheel 14, serve as front running wheels, and a pair ofsteerable running wheels 19, which are connected to pitman arm 159through connection link 166 and so on as shown in FIG. 6, serve as rearrunning wheels. Additionally, axles of steerable running wheels 19 arerunning-driven axles 150L and 150R to which driving forces aretransmitted from running-driving axles 40L and 40R of steerable drivingwheels 47 through sprockets 152 and 153 and chains 154. In brief,steerable running wheels 19 also serve as second running-driving wheels46.

Accordingly, steering wheel 14 is rotated so as to make all front andrear running wheels 47 and 19 differ in their rotary speeds between leftrunning wheels 47 and 19 and right running wheels 47 and 19, andlaterally rotate, whereby the vehicle turns left or right. Preferably,rear steerable running wheels 19 are laterally turned oppositely to thelateral turning direction of front steerable driving wheels 47 which arelaterally turned to the side of rotated steering wheel 14 (into therunning direction of the vehicle).

The vehicle of FIG. 17 is a six-wheel vehicle, wherein a pair of secondrunning-driving wheels 46 are provided as rearmost running wheels inaddition to four steerable running wheels 18 and 47 arranged as shown inFIG. 14 (in this case, steerable driving wheels 47 are laterally turnedoppositely to the lateral turning direction of steerable running wheels18 during rotation of steering wheel 14). Driving forces are transmittedfrom running-driving axles 40L and 40R of steerable driving wheels 47 torunning-driven axles 150L and 150R of second running-driving wheels 46through sprockets 152 and 153 and chains 154.

The vehicle of each of FIGS. 18 and 19 is a six-wheel vehicle having thearrangement of running wheels 47 and 19 (in this case, steerable runningwheels 19 are laterally turned oppositely to the lateral turningdirection of steerable driving wheels 47 during rotation of steeringwheel 14) as shown in FIG. 16. In addition to running wheels 47 and 19,for serving as frontmost running wheels, the vehicle of FIG. 18 isprovided with a pair of castors 16, and the vehicle of FIG. 19 isprovided with a pair of steerable running wheels 18 steered by steeringwheel 14.

Next, description will be given on a vehicle of FIG. 20 having anothertransmitting structure interposed between running-driving axles 40L and40R as output shafts of axle driving/steering unit 10 and another pairof axles.

A pair of left and right running-driven axles 172L and 172R arerotatably supported by vehicle chassis 12 in parallel to left and rightrunning-driving axles 40L and 40R onto which steerable driving wheels 47are attached (in this case, running-driven axles 172L and 172R aredisposed behind running-driving axles 40L and 40R). A differential unit171 is disposed so as to differentially connect left and rightrunning-driven axles 172L and 172R with each other. Onto the outer endsof running-driven axles 172L and 172R are fixed second running-drivingwheels 46. Between motor shaft 54 of main driving HST 21 and an inputshaft of differential unit 171 are interposed transmission shafts 168 aand 168 b in series which are differentially connected with each otherthrough a center differential unit 169, so as to drive secondrunning-driving wheels 46. Steering wheel 14 is operatively connectedwith arm 139 for turning movable swash plate 76 of steering HST 22through pitman arm 159 and connection link 160.

In such the construction, when steering wheel 14 is rotated, left andright steerable running wheels 47 serving as front running wheels areturned laterally conforming with a rotational angle of steering wheel 14and simultaneously, they are given a difference of rotary speedtherebetween through steering HST 22 driven by the rotationalmanipulation of steering wheel 14. Furthermore, second running-drivingwheels 46 serving as rear running wheels are driven substantially insynchronism with the driving of steerable driving wheels 47, therebyenabling the vehicle to travel steadily while exactly applying thedriving force onto the ground without dragging rear running wheels 43.

Hitherto have been described some embodiments of such a vehicle thatsteering wheel 14 is so operated as to generate a rotary speeddifference between left and right running-driving wheels 43 and to turnsteerable running wheels 41 laterally. However, if steering wheel 14 andsteerable running wheels 41 are connected to each other through aconventional linkage, lateral turning angles of steerable running wheelsare restricted because the tilt angle of tie rod 157 is restricted. As aresult, the differential rotation of running-driving wheels 43 cannot beused efficiently, thereby compelling the vehicle to turn on anunexpectedly large circle.

The following steering system and some vehicles employing the steeringsystem, which will be described in accordance with FIGS. 21 to 48, are apreferred solution to this problem.

Description will now be given of a vehicle shown in FIG. 21. Left andright drive axles 40L and 40R are rotatably supported by transmissionhousing 25 mounted on a longitudinally intermediate portion of vehiclechassis 12, and left and right running-driving wheels 43 (43L and 43R)are fixed onto respective outer ends of drive axles 40L and 40R. Leftand right steerable running wheels 41 (41L and 41R) are disposed infront of respective wheels 43. A steering linkage 100 comprises left andright steering gear units 101L and 101R interlocking respective wheels41 to steering wheel 14. Alternatively, steering linkage 100 andsteerable running wheels 41 may be disposed behind transmission housing25 and running-driving wheels 43.

Steering wheel 14 is connected to a center pivotal joint 69 on anintermediate portion of a tie rod 110 through a steering gear box 68.The movement of tie rod 110 according to rotation of steering wheel 14is transmitted through link 160 to control lever 139 for rotatingmovable swash plate 76 of steering HST 22 in transmission housing 25 soas to rotate left and right drive axles 40L and 40R, i.e., first runningwheels 43, at different speeds, thereby turning the vehicle.

As shown in FIG. 22, a hydraulic power steering cylinder 113 may bealternatively interposed between steering wheel 14 and joint 69 so as tochange the rotary force of steering wheel 14 into hydraulic power. Inthis case, a hydraulic control valve 112 for controlling cylinder 113takes the place of steering gear box 68. That is, steering wheel 14 isrotated so as to control valve 112, thereby reducing the manipulatingforce required for rotating steering wheel 14. Also in this case, theswing of tie rod 110 by telescoping of cylinder 113 is transmitted tosteering linkage 100 so as to turn steerable running wheels 41laterally, and transmitted to the transmission in housing 25 throughlink 160 so as to rotate running-drive wheels 43 differentially.

As shown in FIG. 23, the vehicle employing steering linkage 100 may be asix-wheel running vehicle having additional left and right wheels 45Land 45R. Wheels 45L and 45R are fixed onto outer ends of respective leftand right axles 50L and 50R rotatably supported by chassis 12.Alternatively, wheels 45 may be rotatably provided around respectiveaxles 50 fixed to chassis 12.

In FIG. 23, wheels 45 do not receive driving force but rotateindependently of wheels 43. Alternatively, wheels 45 may be rotated bydriving force transmitted from driving axles 40L and 40R as shown inlater-discussed FIGS. 45 to 48. Furthermore, shown steering linkage 100may be provided with the hydraulic power steering system as shown inFIG. 22.

As mentioned above, steering linkage 100 is constructed from steeringwheel 14 to left and right steerable running wheels 41L and 41R throughtie rod 110 and left and right steering gear units 101L and 101R (101,if it is not specified to be left or right) for turning steerablerunning wheels 41 leftward and rightward in connection with thedifferential rotation of first running wheels 43 according to operationof steering wheel 14.

A mechanism of steering linkage 100 will be described on the assumptionthat steerable running wheels 41 are set in a straight traveling state.

Since left and right steering gear units 101L and 101R are constructedlaterally symmetrically to each other, some figures (such as FIG. 25)illustrate one of steering gear units 101. It may be understood that theother omitted steering gear unit 101 is constructed laterallysymmetrically to shown steering gear unit 101.

As shown in FIG. 24, an axle beam 107 is vertically rotatably hung onthe front portion of chassis 12 through a center pin 102 so as to beextended laterally. Left and right sector gears serving as drive gears38 are disposed above axle beam 107 laterally oppositely to each otherwith respect to center pin 102 so as to face their toothed peripherieslaterally distally. Drive gears 38 are pivoted through approximatelyvertical pivot pins 106 respectively onto axle beam 107 so as to besubstantially horizontally rotatable. Left and right pivotal joints 111are attached to respective proximal ends of drive gears 38 (more closeto the lateral middle of vehicle than respective pivotal pins 106). Leftand right rods 103L and 103R (103, if it is not specified to be left orright) are pivotally connected at their one ends to tie rod 110oppositely to each other with respect to center pivotal joint 69, andpivotally connected at their other ends to respective drive gears 38through respective pivotal joints 111.

When steering wheel 14 is rotated from its neutral position (a straighttraveling setting position), tie rod 110 is tilted so that one of rods103L and 103R is pushed forward so as to rotate the toothed periphery ofcorresponding gear 38 backward, and the other is pulled backward so asto rotate the toothed periphery of the other gear 38 forward.

Kingpin supporters 108 are fixed onto left and right ends of axle beam107, respectively. Each of a pair of L-like shaped kingpins 109 issubstantially vertically passed through respective supporters 108 whilebeing allowed to rotate substantially horizontally. Each of kingpins 109is bent and extended laterally distally under supporter 108 so as toserve as a pivot of each steerable running wheel 41.

As shown in FIG. 26, cranked kingpins 116 may replace L-like shapedkingpins 109. Each kingpin 116 is rotatably passed through supporter 108substantially vertically downward, bent laterally proximally between abottom of supporter 108 and a top of tire 41 b of steerable runningwheel 41, extended downward along an inside surface of steerable runningwheel 41, and bent and extended laterally distally so as to pivotsteerable running wheel 41.

In comparison with the case shown in FIG. 24 where steerable runningwheels 41 are disposed laterally outward from respective left and rightends of axle beam 107 with kingpins 109, the vehicle bottom height canbe increased by using kingpins 116 so as arrange steerable runningwheels 41 below axle beam 107 and just under or laterally inward fromthe respective left and right ends of axle beam 107 as shown in FIG. 26.Thus, there is reduced such a problem when the vehicle travels and turnson a rough or soft ground that a bottom of the vehicle is damaged bytouching the ground or the vehicle cannot travel because of slumping ofsteerable running wheels 41. Further, the vehicle can be laterallynarrowed substantially as much as axle beam 107 so that the vehicle cantravel on a narrow road or field.

As shown in FIGS. 24 to 26, each of left and right sector gears servingas follower gears 39 is fixed at its distal end onto the top of each ofkingpins 109 (116) so that each of kingpins 109 (116) serves as a pivotof each of follower gears 39 and rotates substantially horizontallyintegrally with each of follower gears 39.

A proximal toothed periphery of each follower gear 39 meshes with adistal tooted periphery of each drive gear 38 so as to constitute eachof left and right steering gear units 101L and 101R.

Follower gear 39 meshing with drive gear 38 which is rotated so as tomove its toothed periphery forward according to rotation of steeringwheel 14 is also rotated so as to move its toothed periphery forward,thereby laterally turning corresponding steerable running wheel 41 so asto turn its front end distally. This steerable running wheel 41 isarranged on inside of the vehicle in turning. On the contrary, followergear 39 rotating so as to move its toothed periphery backward togetherwith meshing drive gear 38 turns corresponding steerable running wheel41 so as to turn its front end proximally. This steerable running wheel41 is arranged on outside of the vehicle in turning.

On the straight line connecting the fulcrums of both gears 38 and 39(i.e., connecting the center of pivot 106 and the center of kingpin109), a distance of drive gear 38 between its toothed periphery and thecenter of pivot 106 is referred to as a radius R1 of drive gear 38, anda distance of follower gear 39 between its toothed periphery and thecenter of kingpin 109 is referred to as a radius R2 of follower gear 39.Hereinafter, those of drive and follower gears of each of steering gearunits 101L and 101R according to later-discussed various embodiments,e.g., those of later-discussed bevel gears 82 and 83, are referred to asthe same. In each of steering gear units 101L and 101R, radius R1 ofdrive gear 38 is larger than radius R2 of follower gear 39 meshing withthe drive gear 38 so that, when drive gear 38 is rotated, follower gear39 rotates at a larger angle than drive gear 38. Therefore, while thetilt angle of tie rod 110 according to rotation of steering wheel 14 issmall, steerable running wheels 41 can be turned laterally at largeangles.

The pivot of drive gear 38 constituted by pin 106 is parallel to thepivot of follower gear 39 constituted by kingpin 109 (116) so thatmutually meshing gears 38 and 39 are spur gears.

Alternatively, as shown in FIGS. 27 to 29, mutually meshing bevel gears82 and 83 may replace mutually meshing spur gears 38 and 39. Radius R1of bevel gear 82 serving as a drive gear is larger than radius R2 ofbevel gear 83 serving as a follower gear. Therefore, during rotation ofdrive gear 82, follower gear 83 rotates at a larger angle than drivegear 82, so that the lateral turning angles of steerable running wheels41 can be large while the swing angle of tie rod 110 caused by rotationof steering wheel 14 is restricted.

Referring to FIGS. 27 to 29, a pair of bearings 80 are mounted on thetop surface of axle beam 107 adjacently to the respective left and rightends of axle beam 107. Lateral pivot pin 81 rotatably penetrates eachbearing 80. Arm 87 is fixed at its lower end to a proximal end of eachpivot pin 81, and pivotally connected at its upper end to respective rod103L and 103R through pivotal joint 111. Drive gear 82 is fixedly hungfrom a distal end of each pivot pin 81 so as to arrange its toothedperiphery below.

Supporters 79 for pivoting respective kingpins 109 are fixed onto therespective left and right ends of axle beam 107. Each supporter 79 isnotched under axle beam 107. Follower gear 82 is fixed around a verticalintermediate portion of kingpin 109 in the notched space of supporter79, and disposed perpendicularly to drive gear 82 so that the laterallydistal toothed periphery of follower gear 83 meshes with the toothedperipheral bottom of drive gear 82.

When steering wheel 14 is rotated so as to push one of rods 103L and103R forward and pull the other backward through tie rod 110, one coupleof gears 82 and 83 is rotated forward so as to laterally turncorresponding steerable running wheel 41 as one on outside of thevehicle in turning, and the other couple of gears 82 and 83 is rotatedbackward so as to laterally turn corresponding steerable running wheel41 as one on inside of the vehicle in turning.

In comparison with the case where spur gears 38 and 39 are disposedabove axle beam 107, bevel gears 82 and 83 are disposed laterallyoutside or below axle beam 107 so as to ensure a large room in thevehicle body above axle beam 107 for peripheral equipments such aslamps.

Variety of bevel gears 82 and 83 allows positions of steerable runningwheels 41, a height or width of the vehicle or so on to change easily.Such a simple design change corresponds to variation of a vehicle.

Alternatively, as shown in FIG. 30, drive gears 82 may be extendedapproximately downward from respective arms 87. In this embodiment,drive gears 82 are connected at their upper ends to the lower ends ofrespective arms 87 through respective pivot pins 88 above axle beam 107,and extended downward so as to arrange their lower toothed peripherybelow axle beam 107. A pair of cylindrical supporters 87 are fixed ontothe left and right ends of axle beam 107 and rotatably support upperportions of kingpins 109, respectively. Follower gears 83 are fixedaround vertically intermediate portions of kingpins 109 under supporters89, respectively. Toothed periphery of respective follower gears 83 aredisposed laterally proximally so as to mesh with respective drive gears82.

Since gears 82 and 83 mutually mesh below axle beam 107 and laterallyinward from the left and right ends of axle beam 107, the width of thevehicle can be reduced and the room for arranging some instruments aboveaxle beam 107 can be expanded while gears 82 and 83 are do not hindersteerable running wheels 41 so as to allow steerable running wheels 41to turn laterally at sufficiently large angles. Furthermore, the teethof gears 82 and 83 are protected from dust, stones or the like splashedby steerable running wheels 41, thereby preventing gears 82 and 83 frombeing damaged and reducing frequency of maintenance and costs.

Alternatively, as shown in FIGS. 31 and 32(a), left and right drivegears 82 may be interlockingly connected to steering wheel 14 through adifferential mechanism 130 including bevel gears 120, 121 and 122,instead of tie rod 110 and rods 103L and 103R.

A steering wheel shaft 126 is extended from the center of steering wheel14 and a steering column 127 is integrally and coaxially extended fromsteering wheel shaft 126. A connection rod 128 is extended from steeringcolumn 127 through a universal joint 123. A bearing holder 125, which isU-like shaped when viewed in plan, is mounted on the top surface of axlebeam 107 so as to extend backward from shafts 118 and 119. An inputshaft 129 fixedly provided at its front end with input bevel gear 120 isjournalled by a rear portion of bearing holder 125 so as to be disposedperpendicularly to axle beam 107. Input shaft 129 is connected toconnection rod 128 through a universal joint 124.

A left shaft 118 is journalled by a left front portion of bearing holder125 and bevel gear 121 is fixed on a right end of shaft 118. A rightshaft 119 is journalled by a right front portion of bearing holder 125and bevel gear 122 is fixed on a right end of shaft 119. Both gears 121and 122 are disposed perpendicularly to gear 120 and mesh with gear 120.Left and right shafts 118 and 119 are extended laterally distally alongthe top surface of axle beam 107 and journalled by respective bearings79 a projecting upward from respective supporters 79 which are fixedonto left and right ends of axle beam 107 so as to journal respectivekingpins 109. Drive gear 82 is fixed on a distal end of each of shafts118 and 119 so as to interlock gear 82 with steerable running wheel 41through follower gear 83 and kingpin 109, similarly with drive gear 82of FIGS. 27 to 29.

In this embodiment, left shaft 118 is shorter than right shaft 119.Alternatively, left shaft 118 may be longer than right shaft 119.

According to the embodiment shown in FIGS. 31 and 32(a), input bevelgear 120 meshes with bevel gears 121 and 122 behind shafts 118 and 119.Alternatively, it may mesh in front of shafts 118 and 119, as shown inFIG. 32(b). In this case, above-mentioned bearing holder 125 is furtherprovided with a portion for journalling the front end of input shaft 129in front of shafts 118 and 119. Input shaft 125 is extended forwardbetween bevel gears 121 and 122 and journalled by bearing holder 125before and behind shafts 118 and 119.

Since the vehicle does not require such a wide space for swinging tierod 110 and rods 103L and 103R between steering wheel 14 andbevel-gear-type differential mechanism 130 attached on axle beam 107,there is more room available on the vehicle for other instruments suchas lamps therebetween.

The vehicle having the steering mechanism for laterally turningsteerable running wheels 41 according to the embodiment of FIGS. 31 and32(a) (or FIG. 32(b)) is also constructed so that control lever 139 forrotating movable swash plate 76 of steering HST 22 is moved bymanipulating steering wheel 14 so as to drive running-driving wheels 43differentially, thereby laterally turning the main body of the vehicle.

Description will be given of some embodiments of steering gear units101L and 101R in steering linkage 100, serving as a system forcontrolling lateral turning angles of steering running wheels 41.

Spur gears 104 and 114 shown in FIG. 33 serve as spur gears 38 and 39 ofsteering gear unit 101 as shown in FIGS. 24 to 26. Bevel gears 84 and 85shown in FIGS. 34 and 35 serve as bevel gears 82 and 83 of steering gearunit as shown in FIGS. 27 to 32. Each of sector gears 104, 114, 84 and85 has a constant R1 or R2 in the whole range thereof (however manydegrees the sector gear is rotated).

Whether it is according to the embodiment of FIG. 33 or the embodimentof FIGS. 34 and 35, the front end of steerable running wheel 41 turnslaterally inward as the front end of drive gear 104 or 84 and the frontend of follower gear 105 or 85 approach each other (as the rear ends ofthe drive gear and the follower gear go apart from each other).Conversely, the front end of steerable running wheel 41 turns laterallyoutward as the front end of drive gear 104 or 84 and the front end offollower gear 114 or 85 go apart from each other (as the rear ends ofthe drive gear and the follower gear approach each other).

FIG. 33 illustrates mutually meshing spur gears 104 and 114 when theyarrange steerable running wheel 41 in a longitudinal direction of thevehicle for straight traveling. Gears 104 and 114 tangentially contacteach other through a point T on a line between the centers of pivots 106and 109. The toothed peripheral range of drive gear 104 ahead of point Tis named a front central angle range 138, and that behind point T isnamed a rear central angle range 137. The toothed peripheral range offollower gear 114 ahead of point T is named a front central angle range134, and that behind point T is named a rear central angle range 133.

If illustrated steering gear unit 101 interlocks with inside steerablerunning wheel 41, which is positioned at inside of the vehicle inturning, gears 104 and 114 mesh with each other through their rearcentral angle ranges 137 and 133 so as to turn the front end of insidewheel 41 laterally outward of the vehicle. If illustrated steering gearunit 101 interlocks with outside steerable running wheel 41, which ispositioned at outside of the vehicle in turning, gears 104 and 114 meshwith each other through their front central angle ranges 138 and 134 soas to turn the front end of outside wheel 41 laterally inward of thevehicle.

Drive gear 104 has constant radius R1, and follower gear 114 hasconstant radius R2 that is smaller than radius R1. Because of R1>R2, thecentral angle range of gear 114 becomes larger than that of gear 104 ifgears 104 and 114 share the same length of toothed periphery. Therefore,rear central angle range 133 of gear 39 is larger than rear centralangle range 137 of gear 104, and front central angle range 134 of gear114 is larger than front central angle range 138 of gear 104.Consequently, the rotational angle of follower gear 114 becomes largerthan that of drive gear 104, whether they interlock with inside wheel 41or outside wheel 41. Namely, steering gear unit 101 amplifies theallowed lateral turning of steerable running wheel 41.

Since the rotational degree of follower gear 114 which laterally rotatessubstantially integrally with steerable running wheel 41 is alwayslarger than that of drive gear 104, the vehicle can turn on a smallcircle while the rotational angle of steering wheel 14 being restricted,thereby improving the operability for steering. For example, kingpin 109may be rotated 180 degrees while steering wheel 14 is rotated 90degrees.

The same performance is assured in steering gear unit 101 comprised ofbevel gears 84 and 85 shown in FIGS. 34 and 35. However, in this case,both radii R1 and R2 are not disposed in a line. As shown in FIG. 35,radius R1 of drive gear 84 is a substantially downward distance from thecenter of pivot shaft 81 to the abutting surface of gear 84 against gear85, and radius R2 of follower gear 85 is a substantially horizontaldistance from the center of kingpin 109 to the abutting surface of gear85 against gear 84.

Referring to FIG. 40, each of straight line graphs 33 a and 33 bexpresses variation of lateral turning angle of each of inside andoutside steerable running wheels 41 in relation to rotational angle ofsteering wheel 14, in a case where each wheel 41 interlocks withsteering gear unit 101 wherein radius R1 of the drive gear is as largeas radius R2 of the follower gear. Each of straight line graphs 34 a and34 b expresses variation of the same ratio of each of inside and outsidewheels 41, in the case where each wheel 41 interlocks with steering gearunit 101 wherein radius R1 of the drive gear is larger than radius R2 ofthe follower gear. Since graphs 34 a and 34 b are steeper than graphs 33a and 33 b, it turns out that the response of lateral turning ofsteerable running wheels to steering operation is enhanced when radiusR1 of the drive gear is larger than radius R2 of the follower gear as inthe present embodiment.

Each of graphs 34 a and 34 b is straight because it illustrates thevariation of turning angle of each wheel 41 when radius R1 of the drivegear and radius R2 of the follower gear are constant (i.e., the gearratio between the drive gear and the follower gear in steering gear unit101 is constant) as shown in FIG. 33 or FIGS. 34 and 35. Furthermore,graphs 34 a and 34 b are as steep as each other. It means that the rateof variation of lateral turning angle of inside wheel 41 is equal tothat of outside wheel 41.

However, in this case, since the axes of inside and outside wheels 41about their own rotations become parallel to each other, it cannot beperformed that both extensions of axes of laterally turned inside andoutside wheels 41 cross each other at a position coinciding with thelateral turning of the vehicle caused by the differential driving ofright and left wheels 43 regardless of rotational angle of steeringwheel 14. For realizing this performance, there must be a difference oflateral turning angle between inside wheel 41 and outside wheel 41.Moreover, the lateral turning angle of inside wheel 41 must be largerthan that of outside wheel 41.

Then, for realizing such a lateral turning angle difference between thedrive gear and the follower gear, mutually meshing spur gears 58 and 59as shown in FIG. 36 serve as spur gears 38 and 39 of steering gear unit101. Radius R1 of drive gear 58 is larger than radius R2 of followergear 59 regardless of its rotational direction or angle, therebyamplifying the allowed lateral turning angle of wheel 41. However,radius R1 of drive gear 58 varies according to its rotation, andsimultaneously, radius R2 of follower gear 59 varies so as to compensatefor the variation of radius R1.

FIG. 36 illustrates mutually meshing spur gears 58 and 59 when theyarrange steerable running wheel 41 in a longitudinal direction of thevehicle for straight traveling. Gears 58 and 59 tangentially contacteach other through a point T on a line between the centers of pivots 106and 109. The toothed peripheral range of drive gear 58 ahead of point Tis named a front central angle range 148, and that behind point T isnamed a rear central angle range 147. The toothed peripheral range offollower gear 59 ahead of point T is named a front central angle range144, and that behind point T is named a rear central angle range 143.

When arranging wheel 41 in the longitudinal direction of the vehicle forstraight traveling, radius R1 of drive gear 58 is R1 m, and radius R2 offollower gear 59 is R2 m, as shown in FIG. 36.

If steering gear unit 101 shown in FIG. 36 interlocks with inside wheel41, gears 58 and 59 mesh with each other through their rear centralangle ranges 147 and 143 so as to turn the front end of inside wheel 41laterally outward of the vehicle. At this time, radius R1 of drive gear58 is larger than Rim, and radius R2 of follower gear 59 is smaller thanR2 m. As the rear ends of gears 58 and 59 approach each other, radius R1increases and radius R2 decreases so as to compensate for the increaseof radius R1. When radius R1 reaches maximum radius R1 r and radius R2reaches minimum radius R2 r, the lateral outward turning angle of thefront end of inside wheel 41 reaches the maximum.

If steering gear unit 101 shown in FIG. 36 interlocks with outside wheel41, gears 58 and 59 mesh with each other through their front centralangle ranges 148 and 144 so as to turn the front end of inside wheel 41laterally inward of the vehicle. At this time, radius R1 of drive gear58 is smaller than R1 m, and radius R2 of follower gear 59 is largerthan R2 m. As the front ends of gears 58 and 59 approach each other,radius R1 decreases and radius R2 increases so as to compensate for thedecrease of radius R1. When radius R1 reaches minimum radius R1 f andradius R2 reaches maximum radius R2 f, the lateral inward turning angleof the front end of outside wheel 41 reaches the maximum.

Therefore, according to increase of rotational angle of steering wheel14, the gear ratio R2/R1 of steering gear unit 101 interlocking withoutside wheel 41 increases so as to reduce the rate of increase oflateral turning angle of outside wheel 41. Simultaneously, the gearratio R2/R1 of steering gear unit 101 interlocking with inside wheel 41decreases so as to compensate the increase of that of steering gear unit101 interlocking with outside wheel 41, thereby increasing the rate ofincrease of lateral turning angle of inside wheel 41. As a result, thedifference of lateral turning angle between inside wheel 41 and outsidewheel 41 increases as the rotational angle of steering wheel 14increases. Graphs 35 a and 35 b in FIG. 40 express the variation oflateral turning angle of inside and outside wheels 41 in this way.

Referring to FIGS. 37 to 39, steering gear unit 101 comprising bevelgears 175 and 176 is so constructed that, according to rotation ofsteering wheel 14 from the straight traveling position, the gear ratioR2/R1 thereof increases when it interlocks with inside wheel 41, anddecreases when it interlocks with outside wheel 41, similarly to thatcomprising spur gears 58 and 59. In other words, according to increaseof rotational angle of steering wheel 14, the increasing rate of lateralturning angle of inside wheel 41 is increased while the increasing rateof lateral turning angle of outside wheel 41 is decreased so as tocompensate for the increase of that of inside wheel 41. Graphs 35 a and35 b in FIG. 40 also express the variation of lateral turning angle ofinside and outside wheels 41 by steering gear units 101L and 101Rcomprising bevel gears 175 and 176.

For assuring such a variation of gear ratio R2/R1, respective toothededges of drive gear 175 and follower gear 176 are actually bent atapproximately 45 degrees so as to face and mesh mutually. In FIGS. 37and 38, such bent toothed edges of gears 175 and 176 are omitted forconvenience.

Description will now be given of aspects of a vehicle employing left andright steering gear units 101L and 101R of FIG. 36 having variable gearratios, in accordance with FIGS. 41 to 44 and FIGS. 45 to 48.Hereinafter, only left turning of the vehicle is disclosed, however, thevehicle performs similarly in not-shown right turning. Furthermore,steering gear units 101L and 101R comprising bevel gears 175 and 176shown in FIGS. 37 and 38 also enables the vehicle to turn in the sameway.

The four-wheel vehicle shown in FIGS. 41 to 44, having two right andleft steerable running wheels 41 and two right and left running-drivingwheels 43, is identical to the vehicle shown in FIG. 21 wherein variablegears 58 and 59 serve as gears 38 and 39.

As shown in FIG. 41, when steering wheel 14 is set in a neutral positionfor straight-traveling, left and right steerable running wheels 41 aredisposed on respective lines 187 and 191 that are longitudinal withrespect to the vehicle. At this time, both left and rightrunning-driving wheels 43L and 43R are driven at the same speed in thesame direction (in this embodiment, forward).

Left wheel 43L serving as inside wheel 43 which is disposed at inside ofthe vehicle in turning, is decelerated correspondingly to the leftrotational angle of steering wheel 14 from the neutral position, so thatthe rotary speed of left wheel 43L becomes smaller than that of rightwheel 43R serving as outside wheel 43 which is disposed at outside ofthe vehicle in turning. The turning center of a vehicle body 198 causedby the difference of rotary speed between left and right wheels 43 isessentially disposed on an axial line of axles 40L and 40R extended onthe inside of the vehicle in turning (leftward, when the vehicle turnsleft). According to rotation of steering wheel 14, the difference ofrotary speed between inside and outside wheels 43 increases so as tomove the turning center of the vehicle on the extended axial line ofaxles 40 from the exterior of the vehicle to the interior of the vehicle(the lateral middle of the vehicle between left and right wheels 43).Therefore, the radius of turning circle of the vehicle decreasesaccording to the increase of rotational angle of steering wheel 14.

Accordingly, in order to prevent wheels 41L and 41R from hindering theturning of vehicle body 198 caused by the differential rotation ofwheels 43L and 43R (to prevent wheel 41L or 41R from traverse-slipping),the centers of the lateral turning circles of wheels 41L and 41R, whoseradii are extended axes of respective wheels 41, must coincide with theturning center of the vehicle caused by the differential driving ofwheels 43 or be disposed close to the lateral middle of the vehicle morethan the turning center of the vehicle. For reducing the turning circleof the vehicle so as to promote turning of the vehicle, the centers oflateral turning of wheels 41 are preferably disposed close to thelateral middle of the vehicle more than the turning center of thevehicle caused by the differential drive of wheels 43. Alternatively, ifnecessary, the centers of lateral turning of wheels 41 may be disposedapart from the lateral middle of the vehicle more than the turningcenter of the vehicle caused by the differential drive of wheels 43 soas to expand the turning circle of the vehicle.

However, if the traveling speed is controlled regardless of rotation ofsteering wheel 14, the turning center of vehicle body 198 caused bydifferential rotation of wheels 43 moves on the axial line of axle 40according to variation of traveling speed while the rotational angle ofsteering wheel 14 is maintained. It is possible to construct the vehicleso as to reduce the traveling speed according to increase of rotationalangle of steering wheel 14, or to change the ratio of movement of link139 to the rotational angle of steering wheel 14 in correspondence tovariation of the traveling speed, thereby fixing the turning radius ofthe vehicle, i.e., fixing the turning center of the vehicle in relationto each rotational angle of steering wheel 14.

According to steering linkage 100 including steering gear units 101L and101R constituted by gears 58 and 59, as shown in FIGS. 42 to 44, boththe centers of lateral turning of wheels 41L and 41R coincide with eachother on an extended axial line 199 of axles 40 so that a single point196 serves as a common turning center point 196 shared by both wheels41L and 41R. For convenience, the following performance of the vehicleshown in FIGS. 42 to 44, and further, the performance of a six-wheelvehicle shown in FIGS. 45 to 48 will be described on the assumption thatthe turning center of the vehicle is fixed in relation to each rotationangle of steering wheel 14 regardless of traveling speed, and that point196 serving as the turning center of wheels 41L and 41R is intended tocoincides with the center of turning circle of the vehicle caused by thedifferential rotation of wheels 43L and 43R. Therefore, in the vehicleshown in FIGS. 42 to 44, the length of line 199 between point 196 andthe lateral middle point of the vehicle serves as the turning radius ofthe vehicle.

Referring to FIG. 42, when steering wheel 14 is turned left a little,the rotary speed of left inside wheel 43L becomes smaller than that ofright outside wheel 43R while both wheels 43L and 43R rotates forward,However, the rotational speed difference of wheels 43L and 43R is sosmall that the turning center of the vehicle is disposed on an extensionof line 199 outer-leftward from the vehicle. At this time, left wheel41L is disposed on a line 188, and right wheel 41R on a line 192. Alateral turning angle 181 of left wheel 41L is formed between line 188and line 187 shown in FIG. 41. A lateral turning angle 184 of rightwheel 41R is formed between line 192 and line 191 shown in FIG. 41.Point 196, serving as the center of concentric turning circles of wheels41L and 41R, which tangentially contact with respective lines 188 and192, is disposed on the extension of line 199 outer-leftward from thevehicle so as to coincide with the turning center of the vehicle causedby the differential drive of wheels 43L and 43R. The length of line 199between point 196 and the lateral middle point of the vehicle serving asthe turning radius of the vehicle is so large that the vehicle turns ona large circle.

Referring to FIG. 44, by further rotating steering wheel 14 leftward,the reduced rotary speed left wheel 43L serving as inside wheel 43reaches zero while right wheel 43R serving as outside wheel 43 stillrotates forward, so that the turning center of the vehicle caused by thedifferential drive of wheels 43L and 43R is placed on wheel 43L. At thistime, left wheel 41L is disposed on a line 189, and right wheel 41R on aline 193. A lateral turning angle 182 of left wheel 41L is formedbetween line 189 and line 187 so as to be larger than angle 181. Alateral turning angle 185 of right wheel 41R is formed between line 193and line 191 so as to be larger than angle 184. Point 196, serving asthe center of concentric turning circles of wheels 41L and 41R, whichtangentially contact with respective lines 189 and 193, is disposed onleft wheel 43L on line 199 so as to coincide with the turning center ofthe vehicle caused by the differential drive of wheels 43L and 43R. Thelength of line 199 between point 196 and the lateral middle point of thevehicle serving as the turning radius of the vehicle is so small thatthe vehicle turns on a small circle, in other words, the vehicle turnscentering on left inside wheel 43L.

Referring to FIG. 44, by fully rotating steering wheel 14 leftward, leftwheel 43L serving as inside wheel 43 rotates backward while right wheel43R serving as outside wheel 43 rotates forward, so that the turningcenter of the vehicle caused by the differential drive of wheels 43L and43R is placed on the lateral middle point between wheels 43L and 43R. Atthis time, left wheel 41L is disposed on a line 190, and right wheel 41Ron a line 194. A lateral turning angle 183 of left wheel 41L is formedbetween line 190 and line 187 to be larger than angle 182. A lateralturning angle 186 of right wheel 41R is formed between line 194 and line191 so as to be larger than angle 185. Point 196, serving as the centerof concentric turning circles of wheels 41L and 41R, which tangentiallycontact with respective lines 190 and 194, is disposed on the lateralmiddle point of the vehicle on line 199 between wheels 43L and 43R so asto coincide with the turning center of the vehicle caused by thedifferential drive of wheels 43L and 43R. Since point 196 coincides withthe lateral middle point of the vehicle, the vehicle turns centering onits own lateral middle point. In other words, the vehicle spins.

As the above, when each of steering gear units 101L and 101R isconstituted by mutually meshing drive gear 58 and follower gear 59 asshown in FIG. 36, the gear ratio of steering gear unit 101 interlockingwith inside wheel 41 is always larger than that of steering gear unitinterlocking with outside wheel 41 while steering wheel 14 is rotatedeither left or right from the neutral position. Accordingly, in FIGS. 42to 44, lateral turning angles 181, 182 and 183 of left inside wheel 41Lare larger than lateral turning angles 184, 185 and 186 of right outsidewheel 41R, respectively, so that extensions of axes of left and rightwheels 41L and 41R cross each other on the turning side of the vehicle.This crossing point serves as point 196 around which both wheels 41L and41R turn.

Point 196 moves on axial line 199 of axles 40L and 40R from the exteriorof the vehicle on the turning side thereof to the lateral middle of thevehicle according to rotation of steering wheel 14 from its neutralposition. The output rotational speed and direction of axledriving/steering apparatus 10 in housing 25 is controlled in relation tothe rotational angle of steering wheel 14 so as to make the turningcenter of the vehicle caused by the differential drive of wheels 43L and43R coincide with point 196. In this way, running-driving wheels 43L and43R are properly driven so as to turn the vehicle properly along thelateral turning direction of steerable running wheels 41L and 41R. Sinceboth lateral turning forces of steerable running wheels 41L and 41R andthe turning force of the vehicle caused by the differential rotation ofrunning-driving wheels 43L and 43R are concentrated on the substantiallysingle point, each running wheel is prevented from traverse-slippingdamaging the ground surface, whereby the vehicle turns properly andsteadily.

A six-wheel running vehicle shown in FIGS. 45 to 48, which employsvariable gears 58 and 59 serving as gears 38 and 39 of steering gearunits 101L and 101R, is provided at the rear portion thereof withrunning-driven wheels 46L and 46R replacing running wheels 45L and 45R.Wheels 46L and 46R are fixed onto outer ends of respective driven axles150L and 150R rotatably supported by chassis 12. A sprocket (or apulley) 153 is fixed on each of axles 50L and 50R. A sprocket (or apulley) 152 is fixed on each of axles 40L and 40R having each ofrunning-driving wheels 43L and 43R fixed on its outer end. A chain (or abelt) 154 is interposed between sprockets 152 and 153 on each of lateralsides of the vehicle so as to rotate each of axles 150L and 150R at thesame speed and in the same direction with each of axles 40L and 40R.

As shown in FIG. 45, when the vehicle travels straight forward, allrunning wheels 43L, 43R, 46L and 46R are rotated forward at the samespeed by output of axle driving/steering apparatus 10 in housing 25.Steerable running wheels 41L and 41R rotate in the longitudinaldirection of the vehicle.

As shown in FIGS. 46 to 48, in this vehicle, left running-driving anddriven wheels 43L and 46L are decelerated so as to serve as insidewheels of the vehicle in turning while steering wheel 14 is rotatedleftward. The resultant difference of rotation speed thereof from rightwheels 43R and 46R serving as outside wheels of the vehicle in turningcause a vehicle body 200 to turn laterally (leftward, in thisembodiment). The turning center of vehicle body 200 exists on aresultant axial line 201 of all axles 40L, 40R, 150L and 150R, which isextended at the substantially longitudinal middle between axles 40 andaxles 150.

Therefore, in this vehicle, steering linkage 100 is so constructed as toarrange lateral turning center point 202 shared between steerablerunning wheels 41L and 41R. As shown in FIGS. 46 to 48, turning center202 moves on line 201 from the outer left side of the vehicle to thelateral middle of the vehicle 33 according to the increase of rotationalangle of steering wheel 14 from its neutral position.

Namely, axle driving/steering apparatus 10 interlocking with steeringwheel 14 for turning wheels 41L and 41R controls the rotationaldirection and speed of wheels 43L, 43R, 46L and 46R so as to make theturning center of vehicle body 200 caused by the differential drive ofwheels 43L, 43R, 46L and 46R coincide with turning center 202 of wheels41L and 41R moving on line 201 according to rotation of steering wheel14.

By using steering gear units 101L and 101R comprising variable gears 58and 59, the vehicle, even when it is a six-wheel running vehicle, thelateral turning center of steerable running wheels 41L and 41R coincideswith the lateral turning center of vehicle body 200 caused by thedifferential drive of wheels 43 and 46, thereby being able to turnsteadily.

As the above, the foregoing performances of the vehicles shown in FIGS.41 to 48 have been described while the variation of traveling speed ofthe vehicle is ignored, or on the assumption that the turning center ofthe vehicle caused by the differential drive of wheels 43R and 43L isfixed so as to coincide with the lateral turning center of wheels 41Rand 41L when the rotational angle of steering wheel 14 is constantregardless of the traveling speed. However, actually, the turning centerof the vehicle caused by the differential drive of wheels 43R and 43Lmay move according to variation of the traveling speed even if therotational angle of steering wheel 14 is constant.

However, if the movement of lateral turning center of the vehicle causedby differential drive of wheels 43 relative to every rotational angle ofsteering wheel 14 according to the variation of traveling speed of thevehicle cannot be prevented, the positional difference between thelateral turning center of steerable wheels 41 and the lateral turningcenter of the vehicle caused by differential drive of wheels 43 shouldbe reduced as much as possible.

Then, gears 58 and 59 are so modified as to allow steerable wheels 41 toturn laterally considerably freely from rotation of steering wheel 14.For example, gaps between teeth of gear 58 or 59 are expanded or teeththereof are narrowed so as to expand backlashes, thereby allowing gear59 to rotate considerably freely relative to gear 58.

Alternatively, as shown in FIG. 49, an elongated hole 58 a may be formedin gear 58 for insertion of pivotal pin 111 so as to allow gear 58 torotate considerably freely in relative to pulled or pushed rod 103.

Alternatively, as shown in FIG. 50, the width of a key groove 59 aformed in gear 59 may be larger than the width of a key 109 a formed onkingpin 109 to be inserted into key groove 59 a, thereby allowingkingpin 109, i.e., wheels 41, to rotate relative to gear 59.

Such modifications on gears 58 and 59 may be performed on bevel gears175 and 176 for the same purpose.

The above-mentioned construction of the vehicle according to the presentinvention is applicable to such a vehicle as a tractor, a riding mower,a snow removing vehicle and an amphibious motorcar.

Although several embodiments have been described, they are merelyexemplary of the invention and not to be constructed as limiting, theinvention being defined solely by the appended claims.

1. A vehicle comprising: a prime mover; a pair of left and right runningwheels; a transaxle for driving the left and right running wheels, thetransaxle including a first steplessly variable transmission receivingpower from the prime mover, a second steplessly variable transmissionreceiving power from the prime mover, a pair of axles onto which therespective left and right running wheels are attached, and adifferential unit differentially connecting the axles to each other,wherein output power from the first steplessly variable transmission istransmitted to the axles through the differential unit so as to drivethe axles in the same direction, and wherein output power from thesecond steplessly variable transmission is transmitted to the axlesthrough the differential unit so as to differentially drive the axles; aspeed changing operation device operatively connected to the firststeplessly variable transmission so as to cause output power from thefirst steplessly variable transmission; a steerable wheel; and asteering operation device for steering the steerable wheels, wherein thesteering operation device is operatively connected to the secondsteplessly variable transmission so as to cause output power from thesecond steplessly variable transmission.
 2. The vehicle according toclaim 1, further comprising: a pair of left and right steerable wheelsserving as the steerable wheel steered by operating the steeringoperation device.
 3. The vehicle according to claim 2, wherein the pairof left and right steerable wheels are drivingly connected to therespective left and right axles.
 4. The vehicle according to claim 1,wherein the pair of running wheels are steerable so as to be steeredtogether with the steerable wheel by operating the steering operationdevice.
 5. The vehicle according to claim 1, wherein the firststeplessly variable transmission is a hydrostatic transmission includinga hydraulic pump and a hydraulic motor.
 6. The vehicle according toclaim 1, wherein the second steplessly variable transmission is ahydrostatic transmission including a hydraulic pump and a hydraulicmotor.